Vent Length Research Articles

Increasing Body Size after Exploitation in a Population of Timber Rattlesnakes (Crotalus horridus)

At a field site in northeastern New York during a 40-yr study, we measured the body sizes (total length, snout–vent length [SVL], mass) in three intrinsic groups of adult Crotalus horridus: nongravid (N) females, gravid (G) females, and males. We argue that a bounty system in effect for 75 yr caused a probable decline of the largest animals. After this lengthy period of exploitation, we observed that body sizes began to increase. Across 4 decades, the three intrinsic groups were significantly larger in the final decade (2009–18) than in the first decade (1979–88), stabilizing at a mean body mass of »710 g in N females, »870 g in G females, and »1,200 g in males. Mean SVLs of N females (94.1 cm) and males (111.0 cm) in the final 3 decades were significantly larger than their SVLs in the first decade. The body condition index (BCI) increased over time, and the intrinsic groups differed significantly in mean BCI: N females (-0.0764), G females (0.0146), and males (0.0899). Among recaptured snakes, wide fluctuations of body mass were not uncommon as most snakes experienced annual losses as well as gains. Geographic variation in body size of C. horridus is illustrated by comparing our New York population with a northern population (Massachusetts) and a southern population (Virginia). Across the species' range, we suggest that body size could be associated primarily with prey size. Because many populations of C. horridus are slow growing and long lived, correlated effects of exploitation on body size may negatively affect the snakes' reproductive biology and longevity.

Dynamic movements facilitate extreme gap crossing in flying snakes.

In arboreal habitats, direct routes between two locations can be impeded by gaps in the vegetation. Arboreal animals typically use dynamic movements, such as jumping, to navigate these gaps if the distance between supports exceeds their reaching ability. In contrast, most snakes only use the cantilever crawl to cross gaps. This behavior imposes large torques on the animal, inhibiting their gap-crossing capabilities. Flying snakes (Chrysopelea), however, are known to use dynamic behaviors in a different arboreal context: they use a high-acceleration jump to initiate glides. We hypothesized that flying snakes also use jumping take-off behaviors to cross gaps, allowing them to cross larger distances. To test this hypothesis, we used a six-camera motion-capture system to investigate the effect of gap size on crossing behavior in Chrysopelea paradisi, and analyzed the associated kinematics and torque requirements. We found that C. paradisi typically uses cantilevering for small gaps (<47.5% snout-vent length, SVL). Above this distance, C. paradisi were more likely to use dynamic movements than cantilevers, either arching upward or employing a below-branch loop of the body. These dynamic movements extended the range of horizontal crossing to ∼120% SVL. The behaviors used for the largest gaps were kinematically similar to the J-loop jumps used in gliding, and involved smaller torques than the cantilevers. These data suggest that the ability to jump allows flying snakes to access greater resources in the arboreal environment, and supports the broader hypothesis that arboreal animals jump across gaps only when reaching is not mechanically possible.

Patterns of Visual and Ultraviolet Reflectance in Femoral Gland Secretions of Two Desert Lizards

Femoral gland secretions in lizards convey chemical information about the health and social status of the depositing individual. These secretions influence behaviors related to female mate choice and male–male competition, but little is known about how they are first located by lizards in the environment. Secretions are visually conspicuous and can be sighted from a distance by visually adept lizards, but the specificity of secretion reflectance to the depositing species remains unknown. We examined the reflectance spectra of femoral gland secretions from two sympatric lizard species, Aspidoscelis tigris and Gambelia wislizenii, to determine whether secretions could be visually distinguished. Mean reflectance did not differ between species, but A. tigris had higher reflectance in ultraviolet wavelengths. For both species, lizards in better body condition, as determined by the residuals of the relationship between snout–vent length and body mass, had higher ultraviolet reflectance. In summary, our results indicate that femoral gland secretions can be visually discriminated between species if the discriminating lizard is ultraviolet sensitive.

Climatic-niche evolution with key morphological innovations across clades within Scutiger boulengeri (Anura: Megophryidae).

The studies of climatic‐niche shifts over evolutionary time accompanied by key morphological innovations have attracted the interest of many researchers recently. We applied ecological niche models (ENMs), ordination method (environment principal component analyses; PCA‐env), combined phylogenetic comparative methods (PCMs), and phylogenetic generalized least squares (PGLS) regression methods to analyze the realized niche dynamics and correspondingly key morphological innovations across clades within Scutiger boulengeri throughout their distributions in Qinghai–Tibet Plateau (QTP) margins of China. Our results show there are six clades in S. boulengeri and obvious niche divergences caused by niche expansion in three clades. Moreover, in our system, niche expansion is more popular than niche unfilling into novel environmental conditions. Annual mean temperature, annual precipitation, and precipitation of driest month may contribute to such a shift. In addition, we identified several key climatic factors and morphological traits that tend to be associated with niche expansion in S. boulengeri clades correspondingly. We found phenotypic plasticity [i.e., length of lower arm and hand (LAHL), hind‐limb length (HLL), and foot length (FL)] and evolutionary changes [i.e., snout–vent length (SVL)] may together contribute to niche expansion toward adapting novel niche, which provides us a potential pattern of how a colonizing toad might seed a novel habitat to begin the process of speciation and finally adaptive radiation. For these reasons, persistent phylogeographic divisions and accompanying divergences in niche occupancy and morphological adaption suggest that for future studies, distinct genetic structure and morphological changes corresponding to each genetic clade should be included in modeling niche evolution dynamics, but not just constructed at the species level.

How sexual differences affect locomotor performance and metabolism of the Sword Snake: An integrated view from energetics

AbstractIn snakes, behavioral differences between sex and body size can positively influence locomotor performance and metabolic rate. Evidence suggests that larger body size can positively influence the locomotor performance of snakes and affect the metabolic rate of individuals. However, the influence of sexual variation on locomotor performance may not be entirely explained by the variation in body morphology, but also by sexual behavior. Herein, we investigated the locomotor performance, resting metabolic rate, and enzyme activities in the biochemical metabolic pathways of the sexually dimorphic snake Tomodon dorsatus. We used 20 females and 14 males to measure the sprint speed as a proxy for locomotor performance and oxygen consumption to assess the metabolic rate. We also measured the maximum activity of the enzymes: lactate dehydrogenase and citrate synthase in the intercostal skeletal muscle, liver, and heart. Individual snout–vent length was related to tail length, body mass, and sex but was not with the maturity. Males of T. dorsatus are faster than females, and sprint speed and oxygen consumption were found to not be correlated. Males also had higher metabolic rate, while enzyme activities were similar in males and females. These results contributed to understanding the sexual variation in the reproductive behavior of T. dorsatus. Although the results on locomotor performance do not support the hypothesis that locomotion in the species is favored by sexual dimorphism, the increased locomotor performance in males can be explained by courtship behavior. On the other hand, sexual dimorphism and smaller body size can explain the increased metabolic rates in males.

The Influence of Environmental and Physiological Factors on Variation in American Toad (Anaxyrus americanus) Dorsal Coloration

Adaptive coloration in amphibians is widespread and aids in camouflage, communication, and thermoregulation. Understanding the environmental factors that contribute to color variation is important for predicting how changes in climate and habitat parameters may alter amphibian fitness. Studies on toad coloration have focused on genetic elements, dorsal spot patterns, and juveniles, but less is known about the relationship between adult toad coloration and environmental conditions. The goal of this study was to examine dorsal color variation in adult American Toads (Anaxyrus americanus) in Erie County, Pennsylvania, USA, to determine how environmental and morphological factors influence coloration. We conducted visual surveys to sample adult toads across a habitat gradient and recorded several potential predictor variables (i.e., site elevation, substrate type, snout–vent length, and body surface temperature). We calibrated photographs of each toad and quantified red (R), green (G), and blue (B) color values within seven dorsal body regions. We summarized RGB values for each dorsal body region using a principal component analysis and used model selection approaches to select between models containing different predictor variables. The most supported model to explain the variation in color of all dorsal body regions contained only site elevation. On average, the body regions of all toads from higher elevation sites were darker than those of toads from lower elevations, but the amount of variation in dorsal coloration accounted for by elevation was low. Our results suggest that the factors that drive variation in toad dorsal coloration are complex, but that this trait is potentially sensitive to environmental changes.

A New Nurse Frog (Allobates, Aromobatidae) with a Cricket-Like Advertisement Call from Eastern Amazonia

Integrative analyses, long-term studies, and access to remote areas in Amazonia have led to new hypotheses and increased resolution of the systematics and taxonomy of the small nurse frog genus Allobates (family Aromobatidae). During anuran sampling in the Middle Tapajos River region, state of Para, Brazil, we collected data on a new cryptically colored species of Allobates with a cricket-like advertisement call. Here, we name and describe this new species, following an integration of phenotypic, ecological, and molecular analyses. The results of a phylogenetic analysis based on mitochondrial and nuclear DNA placed the new species as the sister taxon of Allobates grillisimilis. Genetic pdistances between the two sister taxa at the 16S region of the mitochondrial DNA ranged from 7% to 9%. A sister-species relationship between the new species and A. grillisimilis is also supported by phenotypic evidence. Adults of the new species are small (snout–vent length 15.2–16.8 mm in males and 16.5–17.7 mm in females), with a dorsum uniformly tan to reddish brown, a dark brown lateral stripe and a white ventrolateral stripe, arms pale tan brown and legs greyish-brown, and venter yellowish colored, with variable extension and shades of yellow, paler on the throat. The advertisement call is a trill with a mean peak frequency of 5830.2 Hz, arranged in series of short, closely spaced, pulses (mean of 24.3 pulses/s), and followed by silent intervals of variable duration. We discuss the putative drivers generating and maintaining the distinctiveness between the new species and the allopatrically distributed sister taxon, and on threats to the persistence of the new species. With this species description, the Middle Tapajos River region is consolidated as having one of the highest alpha diversities for the genus Allobates in Amazonia.

Aspects of the Reproductive Biology and Beeding Habits of Leptodeira annulata (Serpentes, Imantodini) in Eastern Amazonia

We analyzed reproductive and feeding habits of Leptodeira annulata based on a sample of 136 specimens from eastern Amazonia and compared our data with information from the literature of other populations of L. annulata, as well as of Imantodes cenchoa. As a result, we detected sexual bimaturism, a continuous reproductive cycle, and no sexual dimorphism regarding snout–vent length. Anurans represent the predominant food item of L. annulata in the region, and these snakes do not exclude small prey from their diet, behaving as opportunistic feeders. Interspecific differences in relative fecundity between L. annulata and I. cenchoa may reflect body characteristics that would represent adaptations to the different reproductive strategies of the two species. Despite the conservative nature of some features of the life-cycle strategies of L. annulata, we demonstrate that reproductive strategies of the species may exhibit geographic variation based on the results of other studies approaching the same species in other areas of South America. Considering that larger conspecific females show higher fecundity, it is possible that natural selection favors sexual maturity of females to occur later.

Brain Allometry Across Macroevolutionary Scales in Squamates Suggests a Conserved Pattern in Snakes

Despite historical interest in brain size evolution in vertebrates, few studies have assessed variation in brain size in squamate reptiles such as snakes and lizards. Here, we analyzed the pattern of brain allometry at macroevolutionary scale in snakes and lizards, using body mass and snout vent length as measures of body size. We also assessed potential energetic trade-offs associated with relative brain size changes in Crotalinae vipers. Body mass showed a conserved pattern of brain allometry across taxa of snakes, but not in lizards. Body length favored changes of brain allometry in both snakes and lizards, but less variability was observed in snakes. Moreover, we did not find evidence for trade-offs between brain size and the size of other organs in Crotalinae. Thus, despite the contribution of body elongation to changes in relative brain size in squamate reptiles, snakes present low variation in brain allometry across taxa. Although the mechanisms driving this conserved pattern are unknown, we hypothesize that the snake body plan plays an important role in balancing the energetic demands of brain and body size increase at macroevolutionary scales. We encourage future research on the evolution of brain and body size in snakes to test this hypothesis.

A method to evaluate body length of live aquatic vertebrates using digital images.

Traditional methods to measure body lengths of aquatic vertebrates rely on anesthetics, and extended handling times. These procedures can increase stress, potentially affecting the animal's welfare after its release. We developed a simple procedure using digital images to estimate body lengths of coastal cutthroat trout (Oncorhynchus clarkii clarkii) and larval coastal giant salamander (Dicamptodon tenebrosus). Images were postprocessed using ImageJ2. We measured more than 900 individuals of these two species from 200 pool habitats along 9.6 river kilometers. The percent error (mean ± SE) of our approach compared to the use of a traditional graded measuring board was relatively small for all length metrics of the two species. Total length of trout was −2.2% ± 1.0. Snout–vent length and total length of larval salamanders was 3.5% ± 3.3 and −0.6% ± 1.7, respectively. We cross‐validated our results by two independent observers that followed our protocol to measure the same animals and found no significant differences (p > .7) in body size distributions for all length metrics of the two species. Our procedure provides reliable information of body size reducing stress and handling time in the field. The method is transferable across taxa and the inclusion of multiple animals per image increases sampling efficiency with stored images that can be reviewed multiple times. This practical tool can improve data collection of animal size over large sampling efforts and broad spatiotemporal contexts.

Effects of Freshwater Salinization and Biotic Stressors on Amphibian Morphology

Organisms are commonly exposed to numerous stressors that induce behavioral, physiological, or morphological changes in some combination. At northern temperate latitudes, de-icing agents (primarily sodium chloride, NaCl) are a major stressor to species in freshwater ecosystems. Species-specific responses to road salt toxicity range from lethal to sublethal effects, but it remains unclear how these effects interact with biotic stressors. Morphology can be quite sensitive to environmental changes, yet we know little about how it is affected by road salt exposure. We exposed Wood Frog tadpoles (Rana sylvatica) to two road salt formulations (NaCl and a mixture of NaCl, MgCl2, and KCl), each at three concentrations (200, 600, and 1000 mg Cl–/L), crossed with three biotic stressor levels (predator cue, competition, and a no-stressor control). We then measured the impacts on relative morphology (snout–vent length, body width, forelimb length, forelimb width, hindlimb length, hindlimb width) of the emerging metamorphs. Salt concentration and biotic stressors both impacted relative morphology, but their effects did not interact. Exposure to road salts increased relative snout–vent length (SVL) and body width. In contrast, competition induced relatively shorter SVL and forelimb length while predator cues induced relatively longer hindlimbs and narrower forelimbs. This is the first discovery that road salts can induce changes in amphibian morphology and that these effects are independent of changes induced by biotic stressors. Future research should examine the effects on overwintering success and future fitness in amphibians as well as the impacts of salt on the morphology of other aquatic taxa that are being exposed to freshwater salinization.

Biomass and instar estimation of larvae of Phylloicus cressae Prather, 2003 (Trichoptera, Calamoceratidae) in a montane forest stream, northcentral Venezuela

Biological and ecological aspects of organisms are important to understand the role of species in aquatic ecosystems. Measuring growth rate is useful to analyse these aspects through the estimation of instar and biomass in aquatic insects like shredder trichopterans. We aimed to produce allometric relationships based on larval body parts and case dimensions to estimate larval instars and biomass for Phylloicus cressae Prather, 2003. Here, we showed that classification tree analysis and power and exponential models proved that dorsal and ventral length of cases were good predictors of larval instars and biomass for P. cressae. We also found that allometric relationships involving the length of the prothoracic mid-dorsal ecdysial suture were suited for assessing larval instars but performing these measurements on cased trichopterans is difficult without damaging them. So, allometric models like ours, based on case dimensions, are invaluable when dealing with live individuals.

Maternal Body Size and Condition Predict Measures of Reproductive Success and Future Reproductive Allocation in Territorial Eastern Red-Backed Salamanders

Female fitness is often influenced by trade-offs in energy allocated to reproduction or self-maintenance that is dependent upon the life history of the organism. Maternal body size and condition are factors that are often positively correlated with clutch size and offspring size. We investigated whether maternal body size (snout–vent length, SVL) and condition (residual of mass on SVL) could predict measures of reproductive success including clutch size, offspring body size (SVL), and offspring survival in the territorial Eastern Red-backed Salamander (Plethodon cinereus). Brooding females and their eggs were collected and then housed in a controlled laboratory setting. We recorded the number of eggs found with each female and separated offspring from females once hatched. At 40 d after hatching, we measured the SVL and mass of females and juveniles. Maternal SVL, but not condition, was positively related to clutch size and offspring SVL; however, there was no significant relationship between clutch size and offspring SVL, indicating no trade-off between number and body size of offspring. In the laboratory, survival of the offspring to 185 d post-hatching was positively related to maternal SVL and negatively related to maternal condition. Also, the mean SVL, measured on day 40, of the offspring that survived to 185 d was significantly greater than the SVL of the offspring that did not survive, indicating a benefit of larger offspring body size. Finally, subsequent egg production (number of new oocytes produced by females following the current reproductive bout) was positively related to maternal SVL and condition (measured 185 d after hatching their previous clutches). These results suggest that larger maternal body size and condition of Eastern Red-backed Salamanders provide increased reproductive success through the number and body size of offspring produced in current or subsequent reproductive bouts and in offspring survival. Large body size in territorial animals like P. cinereus provides benefits for holding high quality territories as well as for increased reproductive success.

Finding a shadow in the dark: rediscovery of Fugler&amp;rsquo;s Shadow Snake (Emmochliophis fugleri Fritts &amp;amp; Smith, 1969) after 54 years, with comments on its conservation status, distribution, and the tribe Diaphorolepidini

Herein we report the second known record of Emmochliophis fugleri Fritts &amp;amp; Smith, 1969, present the first color images of the species, extend its known distribution and elevational range, provide the snout&amp;ndash;vent and tail lengths of the holotype, and demonstrate that the condition of fused prefrontals is an unreliable diagnostic character for the genus Diaphorolepis. Considering the rarity of this snake as well as the imminent threat that mining poses to the R&amp;iacute;o Manduriacu Reserve, we recommend a conservation status of Critically Endangered for E. fugleri.&amp;nbsp;

Effects of body size, diet, and transience on the demography of the arboreal boid snake Corallus grenadensis on Carriacou (Grenada Grenadines, West Indies)

AbstractRemarkably little is known about the demography of snakes in the family Boidae. This lack of information may be attributed, in part, to low population densities on the Neotropical mainland, rendering capture‐recapture methods impractical for many species. Conversely, islands support fewer species but snake densities can be much higher. Corallus grenadensis is an arboreal boid endemic to the Grenada Bank and, relative to mainland boids, can be amazingly abundant. As young, its diet is comprised largely of native Anolis lizards, a ubiquitous and abundant food source; it then undergoes an ontogenetic shift in diet to a less abundant resource, rodents. From 2015 to 2019, we marked 254 C. grenadensis and used capture–recapture models to estimate abundance, capture probabilities, survival, and the proportion of transients. We hypothesized that the transient effect would increase with body size (snout–vent length [SVL]), prompted by their ontogenetic shift in diet. Capture probabilities increased with sampling effort and decreased with increasing SVL. Abundance ranged from 96 to 141 individuals and annual resident survival was 0.71, 95% confidence interval (CI) = 0.54–0.83. The proportion of transients increased with increasing SVL, with the estimate being distinguishable from zero starting at ~810 mm SVL, coinciding with the size at which their dietary shift from ectothermic to endothermic prey begins. Ontogenetic dietary shifts are widespread in snakes and occur in at least 11 of 17 species of West Indian boids. Thus, the prominence of transients in our study may be indicative of its demographic and ecological importance among other snake species.

Small Volcanic Vents of the Tharsis Volcanic Province, Mars

AbstractDistributed‐style volcanism is an end member of terrestrial volcanism that produces clusters of small volcanoes when isolated magma bodies ascend from broad magma source regions. Volcano clusters can develop over millions of years, one volcano at a time, and can be used to infer unobserved geologic phenomena, including subsurface stresses and cracks during eruption periods. The Tharsis Volcanic Province covers approximately one‐quarter of the martian surface and hosts a large concentration of small volcanoes that formed from distributed volcanism. We present a catalog of 1,106 small volcanic vents identified within Tharsis Volcanic Province. This catalog includes morphologic measurements for each cataloged vent. Vent lengths range from 71 m to 51 km, widths range from 40 m to 3.1 km, and 90% of vents have lengths at least 1.5 times their widths. Additionally, 90% of edifices associated with vents have topographic prominences &lt;100 m. Vents are found throughout Tharsis, though they generally form clusters near large volcanoes or among large graben sets. Older regions with volcanic eruption ages of &gt;1 Ga are found at the Tharsis periphery in the Tempe‐Mareotis region and Syria Planum. Vents in the Tharsis interior have reported ages &lt;500 Ma. Regional trends in vent orientation and intervent alignment are dependent on nearby central volcanoes and fossae. We use these findings to hypothesize that within the most recent 500 Ma, magma was present under and to the east of the Tharsis Montes and that some of this magma erupted and built hundreds of small volcanoes in this region.

Crayfish Eating in Snakes: Testing How Anatomy and Behavior Affect Prey Size and Feeding Performance.

SynopsisQuantifying the performance of animals is a powerful methodology for determining the functional consequences of morphological variation. For example, snakes consume prey whole, and variation in the anatomy of their trophic apparatus directly affects gape and limits maximal prey size. However, for the foraging ecology of snakes and other systems, scant data exist regarding how often maximal capacities are taxed in nature. Hence, we quantified: (1) maximal gape, (2) the size of prey relative to maximal gape, and (3) how the type and relative size of prey affected behavior and prey handling times (HTs) for two species of natricine snakes that primarily eat soft- (Regina septemvittata) or hard-shelled (Liodytes alleni) crayfish. Liodytes alleni had significantly larger maximal gape than R. septemvittata with equal snout–vent length. The percentages of large prey (>60% maximal gape area) consumed in the field were low in both R. septemvittata (22%) and L. alleni (2%). However, R. septemvittata, especially juveniles, ate relatively larger prey than L. alleni. Strategies for dealing with the seasonal scarcity of small crayfish differed as juvenile R. septemvittata commonly removed and ate only chelipeds from crayfish too large to swallow whole, whereas juvenile L. alleni ate many small odonate nymphs. During laboratory trials, unlike R. septemvittata, L. alleni usually used its body to restrain prey with behaviors that depended on relative prey size and prey hardness. Liodytes alleni consumed soft-shelled crayfish significantly faster than R. septemvittata and significantly faster than hard-shelled crayfish. Several of the differences in gape, prey size, and prey HTs and behavior between the crayfish-eating snakes resemble those between two phylogenetically distant species of homalopsid snakes that consume either hard- or soft-shelled crabs. In both groups of crustacean-eating snakes, the decreased capture success in captivity and the rare consumption of relatively large hard-shelled crustaceans in the field suggest that the ability to capture this type of prey constrains prey size more commonly than maximal gape. Based on data integrating snake size and gape with the relative mass of intact prey, the predicted potential feeding performance R. septemvittata consuming intact prey exceeded that of the other three species.

Geographic variation in female body size and clutch size of the lizard Sceloporus variabilis (Squamata: Phrynosomatidae) in Mexico

AbstractThe body size and reproductive characteristics in populations of the same species is influenced by environmental and ecological factors. In this study, we analysed the relationship of environmental factors, morphological characters (body size and mass) and reproductive traits (clutch size) of females from 13 populations of Sceloporus variabilis. Results showed variation in snout‒vent length (SVL), body mass and clutch size among populations. An ANCOVA between SVL and clutch size showed an increase of the latter in females from Alvarado and Valle Nacional; ANCOVA between body mass and SVL revealed an increase in body mass in most populations. A canonical correlation analysis showed a positive relationship between SVL, body mass, and clutch size with elevation and precipitation, but not with temperature. Future studies should assess the effect of seasonality and food resource availability on reproductive investment among populations of S. variabilis to determine whether these characteristics are a function of differences in key ecological factors (e.g. availability of resources and seasonality) associated with each population, and determine the causes of geographic variation in morphological and life history characteristics among populations.

A new species of terrestrial-breeding frog Pristimantis (Anura: Strabomantidae) from the Cordillera del Cóndor, Zamora Chinchipe, Ecuador

ABSTRACT We describe a new species of Pristimantis from the Comunidad Río Blanco, Cordillera del Cóndor, Ecuador. Pristimantis ledzeppelin sp. nov. is characterized by a snout–vent length of 23.9–24.6 mm in adult males (n = 2) and 36.1 mm in one adult female and is compared morphologically with Pristimantis muscosus and other similar species of Pristimantis. The new species is characterized by having skin on dorsum and flanks finely tuberculate to tuberculate, a distinctive scapular fold, skin on venter coarsely areolate; snout rounded with a small rostral papilla; discs on the digits truncate, three times the width of the digits; groin and hidden surfaces of thighs yellowish-cream with distinctive brownish-black marks and/or orange irregular blotches; and coppery red iris.

Sexual Dimorphism and Feeding Ecology of the Black-bellied Bunchgrass Lizard Sceloporus aeneus (Squamata: Phrynosomatidae) in Central Mexico

Morphology and resource use have a significant influence on lizard population dynamics. In this study, sexual dimorphism and feeding ecology were assessed in a population of Sceloporus aeneus from central Mexico. Sexual dimorphism was recorded, with males being larger than females in several morphological characteristics, such as jaw width, femur length, tibia length, and forearm length, but not snout–vent length (SVL) or jaw length, which were similar in both sexes. The stomach contents analysis indicated an insectivorous diet composed of 11 prey categories, of which females consumed 11 and males consumed 9. Low values of feeding niche breadth were found, as well as high overlap between sexes and seasons. For the whole population, adult preys of the family Formicidae and orders Coleoptera and Hemiptera showed the highest values of food importance and abundance. A higher volume of stomach contents was recorded during the dry season than the wet season in both females and males. Results showed a pattern of sexual dimorphism similar to that of other species of the genus Sceloporus, but different from those of other populations of the same species. Morphological variation in jaw length and width seems to be related to food resources use because, in spite of the high similarity in the diet between sexes, the volume of stomach contents was not correlated with SVL in females. These findings suggest a constant consumption of food that is subsequently invested in reproduction. Further studies analyzing morphology and diet and their effect on reproductive characteristics such as clutch size, eggs mass, and volume are needed among populations of this species. The results obtained in this research could help explain the differences and similarities previously reported on the morphology and reproductive characteristics for S. aeneus and other species of the S. scalaris group.